Interdigital line magnetron



April 2, 1963 J. w. MGLAUGHLIN 3,084,280

INTERDIGITAL LINE MAGNETRON Filed Oct. 24. 1960 I N V EN TOR. JOHN W. MCLAUGHL IN ATTORNEYS 3,198 %,230 HflTERDiG-ITAL KNEE MAGNETRQN John W. McLaughlin, San Jose, Qaliil, assignor to Eitel- McCullough, 1112., 5am Carlos, tlalii, a corporation of California Filed Oct. 24, 1963, Ser. No. 64,663 17 iClaims. (Cl. 3l539.73)

This invention relates to magnetrons and, particularly, to magnetrons having an interdigital line forming the radio frequency (RF) interaction means.

One of the types of magnetrons made according to the present state of the art is known as a voltage tunable magnetron, that is, the frequency of the device is controlled by the voltage between the cathode and the interdigital line. Such magnetrons have a construction known as the interidigital line construction, as shown for example in US. Patent No. 2,810,095. This interdigital line consists of an even number of parallel segments disposed in a circular array. According to the prior art the terminals for the segments were limited to two rings disposed around the segments, with every other segment connected to one of the terminal rings and the alternate segments connected to the other terminal ring. The two terminal rings are disposed one at each end of the interdigital line. Since only one of the rings can be at radio frequency ground potential and the other ring is not, a relatively hi h capacitance by-pass is formed between said other ring and another closely spaced electrode in the magnetron. inherently this closely spaced electrode is at the radio frequency ground potential and, the high capacitance between one of the rings and the closely spaced electrode will tap-oif radiofrequency power and return the power to the other terminal ring through the intra-electrode capacitance within the magnetron. Therefore the available radio-frequency power is less than it should be if there were no losses through the intra-electrode capacitance within the magnetron.

An object of the present invention is to increase the amount of available radio frequency power of a magnetron with an interdigital line.

Another object of the present invention is to reduce the capacitance between at least one terminal of the interdigital line and the other electrodes within the magnetron.

Still another object of the present invention is to provide a magnetron with three terminals for the interdigital line wherein one terminal is shielded by the other two terminals.

A further object of the present invention is to provide a means for extending the ground plane of a coaxial line into the ma netron.

A still further object of the present invention is to provide direct connection of a coaxial line to the interdigital line.

Yet another object of the present invention is to provide an improved voltage tunable magnetron.

Briefly described, one embodiment of the invention comprises a magnetron in which the interdigital line has three terminal rings disposed around parallel elongated segments disposed in a circular array with some of the segments connected to the middle terminal ring and the remaining segments connected to the other two.

The invention possesses other objects and features of advantage some of which, with the foregoing, will be set forth in the following description of the invention. The invention is not limited to the disclosed embodiment, as variant embodiments thereof are contemplated and may be adopted within the scope of the claims.

Referring to the drawing:

FIGURE 1 shows in cross-section the voltage tunable magnetron; and

3,0842% Patented Apr. 2, 1963 FIGURE 2 shows a perspective view of the novel inter-v digital line of the magnetron with the other parts removed.

Referring to the drawing in greater detail and to FIG- URE 1, in particular, the magnetron has a cathode support 10 at one end, a collector 12 at the other end, and between the two a cylindrical interaction space 14 formed by the novel interdigital line. The interdigital line is formed by a plurality of thin, elongated segmentslS disposed in a circular array. A hot electron-emitting cathode 16 emits electrons which are guided into the interaction space 14 by a control electrode 18. A magnetic field axially aligned with the interaction space 14 causes the electrons to spiral around a cold non-emitting cathode or electrode 2:), which is at the same potential as the hot cathode 16. The electrons thus travel in an essentially helical path axially along the tube until they are collected on the collector 12 at the other end of the tube. The electrons travel this spirally-helical path because the control electrode 18 is at a positive potential relative to the hot cathode, thereby attracting the electrons radially outward, because the electrons are affected by a force which is perpendicular to the axially aligned magnetic field, and because they are attracted into the interaction space 14 by a positive potential on the segments 15, which potential is more positive than the potential of control electrode 18.

The cathode 16 is preferably a porous sintered-nickel body with barium, strontium, or calcium oxides interposed within the pores and is known as a matrix-type cathode. Other types of cathodes such as a hot emitting filament or a coated oxide cathode may be used instead of a matrix-type cathode. The preferred cathode 16 is mounted between a tubular metallic sleeve 28 and a non emitting metallic radial flange 29, which are in turn mounted on an axial metallic sleeve 30 extending almost the length of the magnetron. Between the axial sleeve 30 and the tubular sleeve 28 is disposed a heating filament 32. The heating filament 32 is preferably a double helically wound type which has its leads connected to a terminal ring 34 and metallic vacuum wall 35, insulated from each other by a ceramic insulator 36. A ceramic backing ring 3"] backs up the metal-ceramic seal at the terminal ring 34, and a ceramic backing ring 38 backs up the metal-ceramic seal at the end wall 35. The terminal ring 34 is also a sealing ring which has a flange 39 turned parallel to the axis of the tube. The axial sleeve 3%, on which the hot cathode 16 is mounted, is preferably of thin-wall construction which acts as a heat dam on one side of the cathode holding the heat of the filament 32 in the region of the cathode 16. The thinwall axial sleeve 30 is mounted at one end on a thin-wall conical support 41 which acts as a heat dam on the other side of the cathode. An aperture '42 is provided in support 41 for easy evacuation. The conical support 41 in turn is mounted on the metallic end wall 35. The other end of the axial sleeve fits over a ceramic rod 43 which in turn fits into a well 44 formed in the collector 12. The cold electrode 20 is concentrically supported on the axial sleeve 39 by two metal rings 46 having apertures 47 for easy evacuation. Thus, the cathode support it), which is one sub-assembly of the magnetron, is formed.

The other assembly of the magnetron comprises the control electrode 18 which is preferably made cylindrical with an inner diameter equal to the outer diameter of the interaction space 14 formed by the segments 15. The control electrode 18 has a terminal ring 48 with a ceramic insulator 51 separating the ring 48 from a metal sealing ring 52. A ceramic backing member 53 is disposed on the opposite side of the sealing ring 52. The segments 15 are mounted so that they form the novel interdigit-al line which has three ring terminals 54, 55,

and 56 and will be described more fully hereinafter. The 48 and the ring terminals 54, 55, and 56 are separated by ceramic insulators 57, 58, and 59, respectively, while an insulator 6% supports the collector 12 to this sub-assembly through the metal ring 61. A ceramic backing member 62 is bonded to ring 61 Opposite the cr'an'iic insulator 60. An'exhaust tabulation '63 is disposed in the collector 12.

Thus, the magnetron is shown preferably made in two sections which are welded together at the edges of flange 39 andlthe sealing ring 52. The cold electrode 20 on the cathode support fits within the interaction space 14 and the ceramic rod 43 fits snugly into Well 44 of the collector, whereby the cathode elements are aligned within the interaction space. The welded envelope is evacuated through the tubulation 63 and then the end of the tubula'tion is nipped-0d as shown.

The magnetron operates in the following manner: An

external magnetic circuit not shown) forms a relatively uniform magnetic field within the interaction space 14 which field is oriented parallel to the tube axis. The hot cathode 16 emits electrons which are attracted by the control electrode 18. The electrons, being thus subjected to a force which is oriented radially outward and perpendicular to the magnetic field, are caused to spiral around the axis of the magnetron. The segments around the interaction space 14, being more positive than the control electrode, attract the spiraling electrons within the interaction space 14. When the electrons .are spiraling within the interaction space, RF. electromagnetic oscillations are formed in the segments in accordance with known theories. The electrons spiral in a somewhat helical path along the axis, and when the electrons reach the end of the interaction space, they are collected on the collector 12 and prevented from re-entering the interaction space 14. This reduces the noise in the radio-freqnency'circuit because out-of-phase electrons are removed from the interaction space.

7 As mentioned above, the segments 15 of the novel interdigital line are connected to three ring terminals, 54, 55, and '56. Referring to FIGURE 2, a perspective vi'ewof the segments 15 and the ring terminals 54, 55, and S6 of the interdigital line is shown. In this embodiment, the interdigi'tal line has preferably eight segments a, b, c, d, e, f, g, and h but more than or less than eight segments may comprise the novel interdigital line without departing froin the invention. Every other segment, segments a, c, e, and g, is connected at a point between its ends to the ring 55 that is disposed between rings 54 and 56. Every fourth segment, segments b and f, is connected at one end to the ring 54 in the manner as shown and the remaining segments a? and h are connected at one end to the ring 56 as shown. The other end of segments b and 7 may also be connected to ring 56 and also theother end of segments d and k may be connected to ring 54. If both ends of segments b, a, f, and h are connected to rings 54 and 56 instead of being connected at only one end to one ring, the electrical characteristics oi the magnetron are improved, but the process for assembling the novel interdigital line is more complicated and expensive. One method for. connecting segments b,'d, f,jand h to both rings 54 and 56 is to braze the free endsfof segments b and f to ring 56 and to braze the free ends of segments d and h to ring St'after the insulating rings 58 and 59 are brazed to rings 54, 55, and 56.

The magnetron which incorporates the novel interdigital line is able to deliver more power than a magnetron which incorporates an interdigital line of the prior art because most of the radio frequency energy is shielded from the other tube electrode by the two rings 54 and 56 which act as ground planes. The rings 54 and 56 acting as ground planes on both sides of ring 55 reduce the RF. leakage currents which are induced in the DC. electrodes in a tube of the prior art. These leakage currents are undesirable because they shunt the RF. energy through the tube thereby decreasing the useful output of the magnetron. Also by applying the novel three terminal interdigital circuit in a magnetron obnoxious RF. radiation is reduced because as mentioned above the ground planes, rings 54 and 56, shield the remaining structure of the magnetron from the R.F. energy by containing the R.F. Within the ground planes. A coaxial line can be readily attached to the novel three terminal line because the center conductor can be connected to ring 55 and the outer cylindrical shield of the coaxial line can be connected to rings 54 and 56 by applying a suitable transition section which encloses the center conductor.

I claim:

1. A magnetron comprising a cathode and an interdigital line, said interdigital line comprising a plurality of segments disposed in a circular array, and at least three terminal rings disposed around the segments, some of said segments being connected to one of said terminal rings which is electrically insulated from the other rings, and the remaining segments being connected to the other said terminal rings.

2. A magnetron comprising a cathode and an interdigital line, said interdigital line comprising a plurality of an even number of segments disposed in a circular array, and at least three terminal rings disposed around the segments, alternate segments being connected to one of said terminal rings which is electrically insulated from the other rings, and the remaining segments being connected to the other said terminal rings.

3. A magnetron comprising a cathode and an interdigital line, said interdigital line comprising a plurality of an even number of segments disposed in a circular array, and at least three terminal rings disposed around the segments, alternate segments being connected to one of said terminal rings which is electrically insulated from the other rings, and the remaining segments being connected to each of the other said terminal rings.

4. A magnetron comprising a cathode and an interdigital line, said interdigital line comprising a plurality of an even number of segments disposed in a circular array, and at least three terminal rings disposed around the segments, alternate segments being connected to one of said terminal rings which is electrically insulated from the other rings, some of the remaining segments being connected to one of said other terminal rings, and the remaining segments being connected to another one of the terminal rings.

5. A magnetron comprising a cathode and an interdigi tal line, said interdigital line comprising a plurality of seg ments disposed in a circular array, and at least three terminal rings disposed around the segments, some of said segments being connected to one of said terminal rings which is electrically insulated from the other rings, some of the remaining segments being connected to one of the other terminal rings, and the remaining segments being connected to another one of the terminal rings.

6. A magnetron comprising a cathode and an interdigital line, said interdigital line comprising a plurality of an even number of segments disposed in a circular array, and at least three terminal rings disposed around the segments, alternate segments being connected to one of said terminal rings which is electrically insulated from the other rings, half of the remaining segments being connected to one of the other terminal rings and the remaining segments being connected to another one of the terminal rings;

7. A magnetron comprising a cathode and an interdigital line, said interdigital line comprising a plurality of seg ments disposed in a circulararray, and at least three ter minal rings disposed around the segments with one of said rings electrically insulated from the other rings, every fourth one of said segments being connected to one of the terminal rings which is axially displaced from the other rings, every first and third one of said segments being connected to the terminal ring which is electrically insulated from the other rings, and the remaining segments being connected to another terminal ring.

3. A magnetron including an evacuated envelope and comprising an anode formed by an interdigital line, a non-emitting electrode disposed through and axially With in said interdigital line, an electron emitting cathode spaced axially from said interdigital line, a control electrode surrounding said emitting cathode, and a collector electrode spaced from and insulated from said non-emit ting electrode and said anode and disposed on the opposite side of said anode from said electron emitting cathode, said interdigital line comprising a plurality of segments disposed in a circular array, and at least three annular terminal rings disposed around the segments and having their outer peripheries outside the envelope, some of said segments being connected within the envelope to one of said terminal rings which is electrically insulated within and outside the envelope from the other rings, and the remaining segments being connected to the other said terminal rings.

9. A magnetron comprising an anode formed by an interdigital line, an elongated non-emitting electrode disposed through and axially Within said interdigital line, and an electron emitting cathode spaced from said non-emitting electrode, said interdigital line comprising a plurality of segments disposed in a circular array, and at least three terminal rings disposed around the segments, some of said segments being connected to one of said terminal rings which is electrically insulated from the other rings, and the remaining segments being connected to the other said terminal rings.

10. A magnetron comprising a cathode disposed on the tube axis and an interdigital line disposed coaxially, said interdigital line comprising a plurality of segments disposed in a circular array, and at least three terminal rings disposed around the segments, some of said segments being connected to one of said terminal rings which is electrically insulated from the other rings, and the remaining segments being connected to the other said terminal rings.

111. A magnetron comprising an anode formed by an interdigital line disposed about an axis, an axially disposed thin-wall metallic sleeve, a tubular non-emitting electrode coaxially mounted on said thin-wall sleeve and disposed within said interdigital line, an indirectly heated electron emitting cathode mounted coaxially on said thin-Wall sleeve and spaced from said non-emitting electrode and from one end of said interaction space, a filament for heating said cathode disposed between said thin-wall sleeve and said cathode, a tubular control electrode disposed coaxially around said cathode, a collector disposed and spaced from the other end of said interaction space, and an insulating rod disposed between said collector and said thin-wall axial sleeve for supporting said sleeve, said interdigital line comprising a plurality of segments disposed in a circular array, and at least three axially spaced terminal rings disposed around the segments, some of said segments being connected to one of said terminal rings and the remaining segments being connected to the other said terminal rings.

12. A magnetron comprising a tubular envelope wall portion to which is attached a collector, an anode, and a control electrode, a sealing ring attached to saidenvelope portion, a second envelope wall portion to which is attached a cathode, and a non-emitting electrode, a second sealing ring attached to said second envelope portion and a vacuum tight bond joining said sealing rings, said collector being positioned adjacent one end of said magnetron and having a well therein opening toward the other end of said magnetron, said anode being formed by an interdigital line and positioned adjacent said collector, said control electrode being positioned adjacent the end of the anode remote from the collector and having a bore therein axially aligned with said Well, a tubular structure disposed coaxially, said non-emitting electrode being a tit) cylinder attached coaxially to said tubular structure and passing through the anode, said cathode being attached to said tubular structure at a position between said anode and the end of the magnetron remote from said collector, a post attached to one end of said tubular structure and fitting snugly within said well in the collector, and mechanical means connecting the other end of said tubular structure to said second envelope wall portion, said interdigital line comprising a plurality of segments disposed in a circular array, and at least three annular terminal rings having their inner peripheries disposed around the segments within the envelope and having their outer peripheries outside the envelope, some of said segments being connected within the envelope to one of said terminal rings, and the remaining segments being connected to the other said terminal rings.

13. A magnetron comprising a first tubular envelope wall portion to which is attached a collector, an anode, and a control electrode, said collector being positioned closing one end of said first tubular envelope wall portion and having a well therein opening toward the other end, a first sealing ring attached to said other end of said first envelope wall portion, said anode being disposed between said collector and said first sealing ring, said anode comprising a plurality of segments supported in a cylindrical array to form an interaction space, at least three terminal rings disposed around said segments, some of said segments being electrically connected together to one of said terminal rings and the remaining segments being connected to the other said terminal rings, said control electrode being positioned adjacent the end of the anode remote from the collector and having a bore therein axially aligned with said interaction space, a second tubular envelope wall portion to which is attached a hot tubular cathode and an axially aligned non-emitting tubular electrode, an end plate closing one end of said second envelope wall portion, a tubular structure fixed coaxially on said end plate, said cathode and non-emitting electrode being mounted on said tubular structure, a second sealing ring disposed on the other end of said second envelope wall portion, a post attached to the free end of said tubular structure, said first and second envelope wall portions being disposed in axially aligned relationship with said first and second sealing rings bonded together, said post fitting snugly within said well, said cathode being spaced axially from said interaction space, and said non-emitting electrode disposed within said interaction space.

14. A magnetron comprising a tubular envelope, a collector, an anode, a control electrode, an indirectly heated tubular cathode, and a non-emitting electrode, said collector being positioned adjacent one end of said envelope and having an axially aligned well therein opening toward the other end of said magnetron, said anode being formed by an interdigital line and positioned adjacent said collector, said control electrode being positioned adjacent the end of the anode remote from the collector and having a bore therein axially aligned, a tubular structure disposed coaxially, said non-emitting electrode being a cylinder attached to said tubular structure and passing through the anode, said cathode being attached to said tubular structure at a position between said anode and the other end of said envelope remote from said collector, a post having one end portion attached to one end of said tubular structure and its other end supported against lateral displacement by the collector, and mechanical means connecting the other end of said tubular structure to said other end of the envelope, said interdigital line comprising a plurality of segments disposed in a circular array, and at least three terminal rings disposed around the segments, some of said segments being connected to one of said terminal rings and the remaining segments being connected to the other said terminal rings.

15. In a voltage tunable magnetron having an evacuated envelope elongated about a central axis, an interdigital anode structure comprising a plurality of circularly arranged metallic anode segments extending axially within said envelope and circurnferentially spaced to provide a plurality of interaction gaps therehetweenyand at least three annular axiallyrspaced terminal rings circumscribing said metallic anode segments, the inner peripheries of said annular terminal rings beingrintegrally connected to selected ones of said anodesegments Within the envelope while being electrically insulated from an adjacent terminal ring and the outer peripheries ofsaid annular terminal rings being electrically insulated from each other.

16. The combination according to claim 15 in which said envelope includes a plurality of axially stacked alternate metallic and dielectric portions, and said annular terminal rings constitute selected ones of said metallic envelope portions with the outer peripheries of the annular terminal members outsidethe envelope and the inner peripheries thereof inside therenvelope.

:17. The conibination;according toclairn .15, in which selected ones of said metallic anode segments have opposite ends integrally connected toalternate ones of said axially spaced terminal rings.

References Cited in the file ofthis patent UNITED STATES PATENTS 2,607,905 Ludi Aug. 19, 1952 2,930,933 Griffin et a1 Mar. 29', 1960 2,941,109 Senior et a1 June 14, 1960 

1. A MAGNETRON COMPRISING A CATHODE AND AN INTERDIGITAL LINE, SAID INTERDIGITAL LINE COMPRISING A PLURALITY OF SEGMENTS DISPOSED IN A CIRCULAR ARRAY, AND AT LEAST THREE TERMINAL RINGS DISPOSED AROUND THE SEGMENTS, SOME OF SAID SEGMENTS BEING CONNECTED TO ONE OF SAID TERMINAL RINGS WHICH IS ELECTRICALLY INSULATED FROM THE OTHER RINGS, AND 